Note: Descriptions are shown in the official language in which they were submitted.
CA 02484573 2007-10-03
1
METHOD OF CLEANING ON IMMERSED-MEMBRANE
FILTRATION APPARATUS
The invention relates to the field of effluent filtration installations,
particularly for
water, for the purposes of its purification and for making it potable. More
precisely, the
invention relates to the field of such installations that include filtration
membranes that are
directly immersed in the effluent to be treated. Yet more precisely, the
invention relates to
a method of cleaning the membranes in such installations.
Immersed membrane installations are characterised by the use of micro-
filtration or
ultra-filtration membranes that may be flat, tubular or with hollow fibres,
generally
grouped together in modules and do not include any housing. These modules are
immersed directly in the treatment tank containing the effluent to be
filtered, and the
permeate is extracted by aspiration. Such filtration installations are notably
described in
the patent US-A-5248424 in the names of Cote et al. in the European Patent
Application
EP-A-510328 and in the article entitled "Direct solid-liquid separation using
hollow-fiber
membrane in an activated sludge aeration tank" in the names of Yamamoto et al.
that
appeared in 1989 in the journal Water Science Technology, vol. 21, pp. 43-54.
The immersed membranes employed in such installations are usually used under
conditions that lead to little clogging at a low trans-membrane pressure that
generally does
not exceed 0.5 bar so as to space apart the cleaning operations for these
membranes as
much as possible. However cleaning operations remain necessary and are
normally
carried out with the help of chemical solutions that are usually hot.
In installations with traditional membranes, in which the filtration modules
are not
directly immersed in the effluent to be filtered, but are fitted with a
housing and equipped
with a filtration loop, the cleaning of the membranes can be easily carried
out without
taking the membranes out of the installation. This type of cleaning, called in-
place
cleaning, consists simply of circulating a cleaning solution in the recycling
loop. Such a
method is effective since it allows good control of the concentration of
chemical product
in the cleaning solution, the temperature of this solution and its contact
time with the
membranes. Furthermore, such a cleaning procedure can be made completely
automatic.
CA 02484573 1996-11-19
2
Finally, the volume of discharge is low and corresponds to the ullage of the
recycling
loop.
However, filtration installations of the type with immersed membranes do not
incorporate either a housing or a recycling loop. One of the disadvantages
associated with
the use of such installations is therefore the fact that the cleaning
operations are made
much more difficult by the absence of such a housing surrounding the
filtration modules
and also by the absence of such a recirculation loop.
Several methods of cleaning such filtration installations with immersed
membranes
have been provided in the state of the technology.
One of these methods, called ex-situ cleaning consists simply of taking the
filtration
modules out of the tank one by one and cleaning them in a device specially
provided for
this purpose. Such a method allows effective cleaning of the membranes to be
carried out
but has a number of disadvantages. On the one hand, it causes the shut-down of
the
installation or a reduction in its efficiency during the relatively long time
required to
transfer the modules into the cleaning device and to carry out the cleaning
operation itself.
In addition, such a method also has the disadvantage of being difficult to
automate which
increases the cost of the method.
It has also been suggested in the state of the technology, to clean filtration
installations with immersed membranes by replacing the effluent present in the
treatment
tank by a cleaning solution and operating the installation in the usual way so
as to allow
passage of the cleaning solution through the pores of the membranes. Such a
technique
also has numerous disadvantages. Although it is effective and can be
automated, this
method, in effect requires the use of a large volume of cleaning solution.
Apart from the
fact that the cost of the reactants is increased, it is more difficult and
also more costly to
heat up such a large volume of cleaning solution. Finally, the volume of the
discharge
(dirty cleaning solution) is also increased.
It should also be noted that, in the state of the technology a method has been
proposed that aims at allowing the in situ cleaning of the membranes of an
installation that
includes such immersed membranes. Such a method, notably described in the
American
patent US-A-5403479 in the names of Smith et al. consists of circulating a
cleaning
CA 02484573 1996-11-19
3
solution through the membranes along a flow path opposite to the filtration
flow and this
without emptying the tank within which the membranes are installed. The
surplus
cleaning solution not passing through the membranes is recycled in such a way
as to
minimise the volume of solution transferred into said tank.
The effectiveness of this method is limited since the cleaning solution used
is
inevitably diluted by the effluent present in the tank as soon as it has
passed through the
membrane, which considerably reduces its effectiveness. At the same time, the
temperature of this cleaning solution reduces equally abruptly as soon as it
has passed
through and this also reduces its effectiveness. In addition, the period for
injecting the
cleaning solution must be limited in time so that the treatment in progress is
not disturbed
particularly since when it is a biological treatment, the biomass present in
the tank can be
quickly decimated if the cleaning solution is injected for too long a time.
Finally, such a
method cannot be employed when the immersed membrane installation under
consideration is used within the context of making the water potable since the
chemical
reactants used in the cleaning solutions are incompatible with such a
treatment.
The object of this invention is to provide a cleaning method for a filtration
installation of the type with immersed membranes that does not have the
disadvantages of
the state of the technology.
More particularly, one of the objects of the invention is to provide such a
method
that can be implemented while keeping the membranes in place in the
installation.
A further object of the invention is to describe such a method of in-place
cleaning
that involves low volumes of cleaning solutions and does not lead to their
dilution.
Another object of the invention is to offer such a method that can be easily
automated.
Yet another object of the invention is to provide a filtration installation
that permits
the implementation of such a method.
These different objectives as well as others that will become apparent in the
following are achieved thanks to the invention which relates to a method of
cleaning a
filtration installation of the type that includes a plurality of membranes
immersed in at
least one tank containing an effluent to be filtered, said method being
characterised in that
CA 02484573 1996-11-19
4
it includes steps consisting of :
- at least partially emptying the effluent contained in said tank in order to
expose said
membranes to the air;
- causing at least one cleaning solution to pass through the pores of said
membranes along
a flow path opposite to the filtration flow of the effluent by passing in said
cleaning
solution from the permeate side of said membranes.
Preferably said method includes a step consisting of recovering or
neutralising said
cleaning solution having passed through said membranes actively employed in
said tank.
Hence, the invention provides an original way of carrying out in-place
cleaning of
membranes of the installation by at least partially emptying the tank in which
the filtration
membranes are installed, in such a way as to allow passage of the cleaning
solution used
from the permeate side of the membranes towards the outside of the membranes
and then
a flow of this solution over the external surface of the membranes to the
bottom of the
tank. In this way, the cleaning solution is used to the maximum of its
capabilities since it
is not diluted on its exit from the membranes and on the contrary it can run
along the
membranes after having passed through their pores.
In addition, such a method allows one to provide uniform distribution of the
cleaning solution on the membranes since there is no counter pressure exerted
against it.
Taking into account the fact that the cleaning solution does not become
diluted after
passing through the pores of the membranes, it is possible furthermore, to use
smaller
volumes of cleaning solutions than those required to obtain effective cleaning
in the
context of the method described above in accordance with the patent US-A-
5403479.
This constitutes another advantage of the method since it will be able to be
used at less
cost.
Although such a method can be used with any filtration installation with
immersed
membranes, this method is advantageously used in installations in which the
membranes
are in a vertical position inside said tank. In effect, such a position
favours the flow of the
cleaning solution over the external surface of the membranes after its passage
through the
pores of the membranes.
In this case, according to a preferred and particularly interesting aspect,
said step of
CA 02484573 1996-11-19
the method according to the invention that consists of causing at least one
cleaning
solution to pass through the pores of said membranes along a flow path
opposite to the
flow for the filtration of the effluent, is carried out by alternatively or
simultaneously
feeding said cleaning solution through the top and through the bottom of said
membranes.
5 Such a characteristic feature allows one to wet the membranes well and, as a
consequence
to use smaller cleaning volumes. On this subject, it should be noted that in
the technique
disclosed by the American patent mentioned above, the cleaning solution is
always fed
through the bottom of the filtration modules.
Advantageously, said method consists of carrying out a cleaning sequence
including at least one step consisting of causing at least one basic cleaning
solution to
pass through said membranes and at least one step consisting of causing at
least one
acidic cleaning solution to pass through the pores of said membranes. The use
of such a
basic cleaning solution and such an acidic cleaning solution allows the
effectiveness of the
cleaning operation carried out using the method according to the invention, to
be further
increased.
Preferably, said method also includes at least one step consisting of causing
at least
one cleaning solution containing an oxidising agent to pass through the pores
of said
membranes. Such a solution could, for example be constituted by a solution of
sodium
hypochlorite or of hydrogen peroxide.
Yet more preferably, said method includes at least one step consisting of
causing at
least one cleaning solution containing a base and a chlorine compound to pass
through the
pores of said membranes and one step consisting of causing at least one acid
cleaning
solution to pass through the pores of said membranes. In effect, it has been
observed that
the use of such a sequence leads to a particularly effective cleaning of the
membranes as
will be explained in greater detail below. Notably such a sequence allows the
use of
cleaning solutions at ambient temperature eliminating the quasi-necessity of
the state of
the technology to heat up the cleaning solutions nornZally used.
Advantageously, said steps of said sequence are interspersed with, followed by
or
preceded by one or more rinsing steps consisting of causing water to pass
within said
membranes.
CA 02484573 1996-11-19
6
Equally advantageously, said method can include at least one soaking step
during
which the supply of cleaning solution is stopped so as to let it impregnate
the membranes
and thereby increase its effectiveness.
Advantageously the cleaning solution or solutions is or are used at the rate
of a total
volume of between 2 and 20 litres per square metre of membrane. These volumes
are
very much less than those used in the state of the technology which are
traditionally of the
order of 50 litres per square metre.
Preferably, the total duration of said cleaning sequence is between 30 minutes
and 4
hours.
The invention also relates to an installation for the implementation of such a
method, said installation including at least one treatment tank inside which a
plurality of
filtration membranes are vertically installed together with means of feeding
an effluent to
be filtered into said tank, means of draining said tank, means of discharging
the permeate
coming from said membranes, at least one storage reservoir for a solution for
cleaning
said membranes, means of feeding said cleaning solution from the permeate side
of said
membranes and which is characterised in that said means of feeding in said
cleaning
solution include means that allow said cleaning solution to be supplied
alternately or
simultaneously through the top or through the bottom of said membranes.
According to an interesting variant of the invention, this installation
advantageously
includes at least two treatment tanks assembled in parallel each having on the
inside, a
plurality of vertically installed filtration membranes, and that it includes
means that permit
the cleaning of the membranes of the first tank and means that permit the
contents of this
first tank to be stored in the second tank during the cleaning.
Preferably such an installation includes means of connecting said drainage
means
with said supply means.
The invention as well as the different advantages that it offers will be more
easily
understood thanks to the description that follows of a non-limitative way of
implementing
the invention that makes reference to the drawings in which :
- Figure 1 represents a diagram of a first embodiment of an installation
conforming to this
invention ;
CA 02484573 1996-11-19
7
- Figure 2 represents a diagram of a second embodiment of an installation
conforming to
this invention ;
Referring to Figure 1, the filtration installation represented includes a
treatment tank
1. This tank is, as usual, fitted with means 2 of feeding in the effluent to
be filtered that
includes a shut-off valve 2a and means of draining the tank 5 that include a
shut-off valve
5a. The installation is continuously fed with water to be filtered through the
valve 2a
controlled by the water level in the tank.
A plurality of membranes 3, organised in a module 4, are installed vertically
in said
tank. In the embodiment described, these membranes are constituted by ultra-
filtration
membranes made up of hollow fibres with filtration from the outside to the
inside, and
assembled into a module of 12 mz.
The installation also includes an aspirating pump 6 that allows the extraction
of the
treated effluent constituted by the permeate from the membranes, through a
network of
channels 7, 8, 9, 10, 15 and 19. The installation further includes three
reservoirs 11, 12,
13 for storing cleaning solutions, each fitted with a shut-off valve 11a, 12a
and 13a, as
well as means that include a set of channels 14 15 and a set of valves 16, 17,
18 that
permit these cleaning solutions to be fed into the foot of the module 4, that
is to say to the
bottom of said membranes 3. Conforming to the invention, the installation also
includes
means that include a channel 19, a valve 20 and channels 8, 9, 14 and valves
16, 17 and
18 that allow the cleaning solutions to be fed into the head of the module 4,
that is to say
to the top of the filtration membranes 3. Finally, it should also be noted
that the content of
the tanks is connected to a supply of mains water 21 fitted with a shut-off
valve 22.
In filtration mode, the shut-off valve 2a for the means 2 supplying the raw
effluent
to the tank 1 is open and the shut-off valve 5a of the means 5 to drain the
tank is closed,
the effluent therefore filling the tank 1 in such a way that the filtration
membranes 3 are
submerged. In addition, the valve 20 is actuated so as to put channel 7 in
communication
with channel 8 and valve 18 is actuated to put channel 15 in communication
with channel
19. Finally, valve 16 is actuated to put channels 8 and 19 in communication
with channel
9 and valve 17 is actuated to put channel 9 in communication with channel 10
for
discharging the permeate. Hence the permeate is drawn off from the head and
from the
CA 02484573 1996-11-19
8
foot of the module 4 at the same time.
When the membranes 4 are clogged and must be cleaned, the installation is
operated
according to the cleaning method of the invention. The cleaning solutions
contained in
reservoirs 11, 12 and 13 can then be used to unclog these membranes and can
advantageously be injected alternately through the top and through the bottom
of the
membranes. It will also be noted that the cleaning solutions could also be
injected
simultaneously through the top and through the bottom of the membranes.
According to the first step in this cleaning method, the tank 1 is drained by
closing
shut-off valve 2a of the means supplying effluent to the tank 1 and by opening
the shut-
off valve 5a of the drainage means 5, in such a way as to allow the discharge
of the
effluent from the tank and to permit the membranes to be exposed to the air.
According to the second step consisting of carrying out the cleaning cycle
itself, the
three cleaning solutions are used one after the other.
For example, if one chooses to first use the solution contained in reservoir
13, as
shown in Figure 1, valve 13a of this reservoir is opened (the valves 11a and
12a of the
other reservoirs remaining closed). Concomitantly, valve 20 is closed, valve
16 is
actuated in a way that puts reservoir 13 in communication with channel 9,
valve 17 is
actuated in a way that puts channel 9 and channel 14 in communication, and
valve 18 is
actuated in a way that puts channel 14 in communication with channel 15. In
this way, the
cleaning solution arrives through the bottom of the membranes and propagates
in
ascending fashion over the entire height of the membranes. The flow rate of
this solution
is obviously calculated to permit good wetting of the membranes. The cleaning
solution
passes easily through the membranes, since there is no liquid capable of
exerting a back
pressure present in the tank. The solution then flows along the membranes.
After having
passed through the membranes, the cleaning solution, made dirty by the
impurities
present on the membranes is discharged through the means 5 for draining the
tank 1. It
should be noted that it is equally possible, in other implementation modes of
the method
according to the invention, not to discharge the cleaning solution or
solutions from the
tank but simply to neutralise them.
After a given time for supplying the cleaning solution through the bottom of
the
CA 02484573 2007-04-20
9
membranes, this same solution can subsequently be fed through the top of the
membranes in a way that increases the effectiveness of the cleaning and in
order to
complete the wetting of the membranes. To this end, valve 18 is actuated in a
way that
puts channel 14 in communication with channel 19 and valve 20 is actuated in a
way that
puts channel 8 in communication with channel 7. The cleaning solution is then
fed in
through the top of the membranes. After having passed through them it flows
along the
membranes and is discharged through the drainage means 5.
After having used the cleaning solution contained in reservoir 13, the
cleaning
sequence can be continued by then using the cleaning solutions contained in
reservoirs 12
and 11 by also feeding them alternately through the top and through the bottom
of the
membranes 4. On each change of cleaning solution, mains water or the permeate
can be
used to rinse the channels through which this solution passes. In addition, it
should be
noted that for each step in the cleaning sequence, the supply of cleaning
solution may be
stopped (by closing the relevant valve 11a, 12a or 13a and switching off the
pump 6) so
as to allow time for the membranes to be soaked by the cleaning solution.
The installation in accordance with Figure 1 has been operated according to
several
cleaning sequences, No. 1, No. 2, No. 3 and No. 4 details of which are shown
in Table
1 below, after the membranes have been clogged by water from the Seine (30
NTU) or
with residuary urban water. For the Seine water, the first three sequences
(1,2,3) have
been carried out with an empty tank and the last one (4) has been tested with
an empty
tank and a full tank. For the residuary urban water, sequence 1 has been
tested with an
empty tank and a full tank.
All these cleaning sequences consist of a base step, an acid step and a
chlorine step
with the exception of the last sequence for which only two steps have been
implemented
(sodium hypochlorite and acid). To put it more clearly, in sequences No. 1,
No. 2 and
No. 3, three cleaning solutions have been applied successively : a first
solution containing
a base, a second solution containing citric acid at 0.5% and a third solution
of sodium
hypochlorite at 0.03%. In sequence No. 4, only two cleaning solutions have
been used :
a first solution constituted by mixing in aqueous solution a base and 0.03%
sodium
hypochlorite solution and a second solution of citric acid at 0.5%. Between
each cleaning
CA 02484573 1996-11-19
solution, the membranes were rinsed with mains water, this being fed into the
tank using
channel 21 and shut-off valve 22.
In addition, in sequences No. 1, No. 3 and No. 4, supply through the top and
then
through the bottom of the membranes was carried out for each cleaning solution
and for
5 each rinsing with flow rates of 100 1/h and for supply times varying from
2.5 to 30
minutes.
With regard to sequence No. 2, only a supply though the bottom was carried out
at
a flow rate of 2501/h and with supply times of 30 minutes for the basic
cleaning solution,
minutes for the two other cleaning solutions and 5 minutes for the rinsing
with mains
10 water.
Finally, in sequences No. 2 and No: 3 soaking times varying from 15 to 40
minutes were applied after injection of the cleaning solutions.
CA 02484573 1996-11-19
11
E E
E
a O O rl a Lrl ttl Lf1 O ri
r~ O O 0 0 N M r-{ 0 = 0 = Q1 N
0 O *"iLn''{ lnN 0 N N N N N =
> O >
'{
E
0
0 r-i V F+"
~ G
E E E E
0 CT .1-7 ~ ~ O o ~
~
O H tr ~ o N U U M M ~ M M
N lD
LO -q
7
0
~ CJl
.~
E E
ro ~ ~ x F
b
Ln in
~ cn LO
~ 0
E E E E
Ul E E E E
~
~
~+ ~ N Ln Q.I O
~ ~ N N '~ N ~ Q~ M tll l11 ~
. ~ U1 . ~{ ~ O ;,a O
E 0 0 0 0
L 0 w w w w
0 4-4 w 4-4 N w
0 =.V
J-j
O i-i 0 0 o ~p O ~p 0
0 0 ~ 0 0 LC1 Lfl
-r-i ~ rl r-i o N N N N N
~
Q) F." =~i _~'" -r-I -ri a+
E ~
u ~" E Lr) ,n Ln Ln
~ P4 M N ~4 N ~ ~ ~
a
~
.,0.~ 0 0 O 0 0 A m w w I
"4 w
~ P4 a
0 0
~ H
U r"~ ,_.{
0 0 p
0 0
0 0 0 0 ~
0
aO q ow
L'1
r-i "I
3 r M
0 Ul ~U O Q) O
(Ii rG o Ci,
H ~ y 3 3 0 -L) ? 3 U 3 0
f
~ U] 'v: U G1 ft$ C7
O CQ
a) ~ ,4 rz rd u
E rti b ? O ~4 2 rtl
~4
~
~ M -~
C)
04 ~
N M
~ r-i d'~ Vl QJ ~ Li ~--! (N M .-M L'l C)
CO
O E
0
~ I
y I > U
C) O ~ Z N
Z ( I
U)
I C
CA 02484573 1996-11-19
12
L,
E
~ m 0 o ~D r U E
Q ,-1 u1 r-I = 3 ,,,i
>
~
L
O
ji E E ~ E E E E ~ U q~ ~
E ~ =~
E, 4 Ln ~ Ln ~ ~ N E E -E E E ,0, m o
r-i
1 O ~ 0 l11 0 U~ N
U l ~ 0 ~ 4
Q D r') 01
VJ Vi N
# # N N 1~
# # # 7 q 0
# # q -.i C
o O 1-1
~
E rn
0
~ N N N.k b d
~ Z p y ~
U1 # # # N ~
Cil m cu
u
1-- #
00 r, un CL o U ~ r 04 Q N -H N ~ ~)4 E E C
Ol u7 rJ
v r~ ~ L7 ~ Lfl V7 r~' S-i N
C~12 Sa Q S-i 0 0 ~ 7 E a
E W W 4-1 W 0 E 0 E
Q 4-4
.~ Q 0
=-~-~ ~ .L~ L 0 4,) Q7
\ \ ~ 0 A m ~
??----" 4-1 11
rI 0 0 o m "Q
o r--i o 0 o O =~ N.r. .s.
H o a O
7;
41
ct
A ~ ~ q a ~ =~
~,
N # Ln E Ln a ~ "U
O N ~ N rl ~ N r-! O~M ro l.t
p E
ID4 ri ~4 LI1 ~4 Ln 01 ~4 ~4 O L - V! a
N ~-I 0 ~-I 0 ~1 Z~11 Q Q 4-1 O CJ :-~
.. ! Q 44 Q 44 Q 4.4 44 A y:3 Na)
04 Q - '"4 4-a Ra r
p E
\ o\ o\ o c o
o H o
(ll ~ o ~ o ~ o o e ~
o ,-1 o ~ o
=~ r~ rf ~ r X 7-.i
J -x rCi U ~
re o -,
w G o a -~
6~o M o~ OJ ul U
75 Li ul 4
Q S4 14 C'"? I N = "4 O N.U N
~ L] ~J i N O I U! O N ,
Cw y
U ~ e~ 3 ~ 3 E a0
cA U U G U U U ~ E
~ ~ p L~ r3 n G ~ rt3 m ~ ~ L' vH
U -~t O ::j j U Z .,-~.{ U 7 ~ O. o N m
~ ~ x o
a ' ~ z uUi I a rUn ~ + cUn ~ m
H w
0 0
u
Q ~ o n
-L3 r! N M ~ L~l ; CO
~
c~
LO F O
u
? ~
Q * O v
V] ~'~ ~ + cn cti
CA 02484573 1996-11-19
13
These different cleaning sequences have been implemented in the course of
different
cleaning operations after the membranes have been clogged with water from the
Seine as
described in Table 2.
Cleaning sequence No. 1 has been implemented for a cleaning operation in which
1%
sodium hydroxide at 25 C (pH = 11.7) has been tested as the basic cleaning
solution
(cleaning operation No. 7)
Cleaning sequence No. 2 has been implemented for a single cleaning operation
in which
the base used as the basic cleaning solution was 1% sodium hydroxide at 25 C
(pH =
11.9) (cleaning operation No. 2).
Cleaning sequence No. 3 has been implemented for two cleaning operations
(cleaning
operations No. 8 and No. 9) in which the base used as the basic cleaning
solution was
1% sodium hydroxide at 25 C (pH = 11.9).
Cleaning sequence No. 4 has been implemented for three cleaning operations in
which the
base used as the cleaning solution containing both a base and sodium
hypochlorite was
0.5% sodium hydroxide (cleaning operations No. 12, 14 and 15)
All these cleaning operations have been carried out, according to the
invention, with the
tank 1 empty. Only cleaning operation No. 15 was carried out, for comparison
purposes,
with the tank full of effluent.
During these different cleaning operations, different volumes of cleaning
solution have
been used ranging from 4.6 to 23.3 1/m2.
Two cleaning operations were also carried out after the membranes had been
clogged with
residuary urban water and activated sludge, as described in Table 3.
In the course of these two cleaning operations (cleaning operations No. 16 and
No. 17),
the cleaning sequence used was sequence No. 1 with ULTRASILTM at 60% as base.
Cleaning
operation No. 16 was carried out in accordance with the invention (empty tank)
while
cleaning operation No. 17 was carried out for comparison purposes with the
tank full.
The quality of the cleaning operations carried out was evaluated on the one
hand by
calculating the percentage permeability of the membranes to mains water after
cleaning in
relation to the permeability of new membranes and, on the other hand by
evaluating the
increase in permeabil'rty of these membranes.
CA 02484573 1996-11-19
14
Table 2 gives the results obtained with water from the Seine. Table 3 gives
the results
obtained with residuary urban water and the activated sludges.
CA 02484573 1996-11-19
H Q)
ro
U! O C) 0 O~ L(1
W O~
~6 ro N J~ 01 H (*1
N N G 4
~+ ro
~+ U C1 E
N C 4 C14
P+ -rl ~- ..7 r-,
~r N
~
0 A ro ch N n ,-i o
r0 3 N cz rn M rn rn rn in
E v
~+ -L-)
a ro G
~-4
U
C) \ = L[1 d' N N O ri O
U1 O Lo r-4 c~ C9 ri CD O
5 4a ri \
~S U
3 3 >. u
~ 0 O w
Q 4-.I H a
0
~~=1 ro N~ r~ Q1 m o N n
rn rn rn rn r
L~ Sa ?a
-~
E (1) .J ~ Q; rE
Q 1.a
N r6 ~J r-i
-i ~N' a 3 A U
~4
~4
N a~ ~ C G C x X
U
-+ ~ m ro ro ro m o
U r-1 y ij u L u I.+ (t
v
r'-I == 1J ~.J L JJ L iJ r-~
N s1 a o, a a a ,-+
_! E E E E
u
r-i 0 N a a U a) a e w
~j
~
U ~ -~= ~~ r~ Ln ~ in c=i
0 m i N ~ r ~ M c ~
~ 4-4 w ~ a
N
w ol y)
p y4 w ao w
p O 3 rn r- rn~ o G o ~ o
S~-I F~a I~.I o
D D D O
ui tn in ~ t!l tf1
~4 u U D4 U o lP U dp
a~ M a a ~õ a
R o ., o , o o . + ~ ~ + ~
~ p 0 ~~ zDw z p 2 2a, x x
44 U a, O U O U 0 U
~ ~ ~ ~ 0 ro C1 (,~ D o (p D
-Lj w zL-, zL'-, Z m
44 H -~ h Ul N N N
a 3 + J-?
Q) Q) r =
r I
N 0~ U~ U N -i r * ~ e v
~ 0 ~
(1) p .
'v~i z
~ 01 Q,
ua
~ o
v z
61
0 w ro
U U O
t
CA 02484573 1996-11-19
16
S.~
=rl ~
ri S.+ ~ IC
===i N f=I ~ L'1
c6 RS N a r. ~
N Ql R ~;..i --'
$+ U GL E
(D a a
a)
=,q m 0-
~
=.~ S~ A
1~ A tC E "~ o
rtl 3 m o n
O E 0) ~
S4 :J
w m G
,~ HI
C>
U
mr-4 ~4 C a c~~i
= 1 N
L~ ~ o i~ ai E
V"4 r'=i \
~ rtS U ~
y-7
-r=I O~ (71 A
~ tAtl y CtJ -=~=i 1- ~
0 ~ ~4 6 O t0 n= '-1 ri
LI 1] t;-1 47 ~
~ o -i
71 Nr m
~ m
41 Lfn
U
CL)
r-4 N 1 N ~ 3
U
u ~4 z
O
~4
C(1
0
ul
p- m
V~~
C)
Li
id
LL4 ~
-4 { 0 F~ ~ ~
4 t
IN N ..
}4
ri (ll et
o
:,-4 Q) H M
~14 -~ U
L l CL)
O ~ I U
LL-4
N I ' T
~D -r'
iU 0 ' j
CA 02484573 1996-11-19
17
These results show that the method of cleaning according to the invention,
compared with
the cleaning operation that consists of filling the tank with washing
solutions, allows one
to reduce the volumes of chemical reactants while maintaining excellent
effectiveness. In
effect, within the context of the invention, it may be observed that the
permeability of the
membrane measured after the cleaning operations is close to or equal to that
of the new
membrane.
In addition, the results also allow it to be shown that the injection of
reactant alternately
through the top and through the bottom (cleaning operation No. 7) is more
effective than
when the reactant is simply injected from bottom to top (cleaning operation
No. 2).
The prudent combination of the different reactants during the different
cleaning sequences
permits a reduction both in the volumes of reactant and the cleaning time.
In particular, the cleaning operations carried out in accordance with washing
sequence
No. 4 using a first cleaning solution containing both sodium hydroxide and
chlorine are
shown as being particularly effective (cleaning operations Nos. 12 and 14)
These results also reveal a cleaning effectiveness that is significantly
greater within the
context of the invention when implemented with the tank empty than when this
cleaning is
carried out with the tank full (cleaning operations Nos. 15 and 17).
Referring to Figure 2, a second embodiment of an installation is shown that
permits the
cleaning of membranes in accordance with the method of the invention without
interruption of its use in filtration mode.
In addition to a distribution system for the cleaning solutions that is
similar to that for the
installation described above, this solution to the problem has four treatment
tanks 1 a, lb,
ic, 1d with a plurality of filtration membranes (hollow fibres) organised into
modules 3a,
3b, 3c and 3d, installed inside each one.
These modules can be supplied in turn with cleaning solutions thanks to valves
18a, 18b,
18c, 18d (for supplying through the bottom of the membranes) and thanks to
valves 20a,
20b, 20c, 20d (for supplying through the top of the membranes).
The means 2 of supplying the tanks with effluent to be filtered include a
buffer reservoir
23, a general shut-off valve J and a shut-off valve A, B, C, D for each
treatment tank. As
for the means for draining the tanks, there is a general shut-off valve I and
a shut-off
CA 02484573 1996-11-19
18
valve for each tank E, F, G, H. Finally the drainage means and the supply
means of the
tanks are connected to one another by a channel 21 a fitted with a shut-off
valve K, that
allows one at will, to transfer the volume drained from one tank into the
other tanks and
vice versa.
When the installation is operating at full capacity, the four tanks 1a, lb, lc
and ld are
supplied with effluent to be filtered. For this purpose, shut-off valves J and
A, B, C, D
are open while the drainage valves E, F, G, H, I and the valve K are closed.
When one wishes to clean the membranes of one of the tanks, for example tank
Id, the
general supply valve J and the valve D for supplying the tank are closed and
the valves H
and K are opened, the other valves remaining in the same condition as
previously. The
general supply valve J being closed, the effluent to be filtered that comes
into the
installation is stored in the buffer reservoir 23. In embodiments where the
content of the
tank is active(for example when it contains activated carbon or activated
sludges) the
volume of effluent present in tank 1 d is drained from this tank and
transferred into the
three other tanks la, lb and lc while the filtration continues.
Once the contents of tank ld have been completely transferred into the other
tanks, the
drainage valve H and valve K are closed and valve J is opened. The cleaning
solutions
can then be fed into the empty tank ld from reservoirs 11, 12 and 13
alternately through
the bottom and through the top of the membranes.
When the cleaning sequence is finished, valve H and valve I are opened to
discharge the
dirty cleaning solutions present in the bottom of tank 1 d. Then the tank can
be rinsed by
simply opening the valve D that supplies the tank.
So as to once again fill tank ld with effluent to be treated with the surplus
of effluent
present in tanks la, lb and lc, supply valves A, B and C are closed and the
drainage
valves E, F and G are opened. The drainage valve H of tank ld is closed as are
the
general supply valve J and the general drainage valve L. So as to allow the
transfer of the
surplus from tanks 1 a, lb and 1 c into tank 1 d, valve K is opened.
Finally in order to allow the installation to return to normal filtration
operation, valves A,
B, C, D and J are opened and the other valves closed.
Such an installation therefore permits implementation of the method of
cleaning
CA 02484573 1996-11-19
19
membranes according to the invention, while preserving the useful content of
the
treatment tanks.
Therefore, the invention provides a cleaning method that can be easily
automated and that
uses undiluted cleaning solutions in small volumes as well as an installation
for
implementing the method.
The embodiments of the invention described here do not have the objective of
reducing
the extent of this patent application. It will therefore be possible to bring
numerous
modifications to the invention without departing from its scope. With regard
to the
method, one can envisage the use of cleaning solutions other than those
indicated, as well
as other types of membranes. With regard to the installation, one can provide
a number of
different tanks and pumping circuits that allow the filtration to continue
during the
cleaning of the membranes of a tank.
